1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive actuator. More particularly, the present invention relates to a piezoelectric/electrostrictive actuator with suppressed inhibition of piezoelectric displacement and improved insulation durability under high humidity atmosphere.
2. Description of Related Art
A piezoelectric/electrostrictive actuator has an advantage that it can precisely control its displacement in submicron order. Especially, a piezoelectric/electrostrictive actuator with a sintered body of piezoelectric/electrostrictive porcelain composition used as a piezoelectric/electrostrictive body has advantages of high electro-mechanical conversion efficiency, large force generation, high response speed, high durability, and low power consumption, in addition to the advantage that it can precisely control its displacement, and it is adopted as an inkjet head, a micro-pump and the like by use of these advantages.
However, in the art, concern about degradation or insulation breakdown of piezoelectric membrane (piezoelectric body) under high temperature and high humidity has been conventionally existing and, in order to suppress such degradation or insulation breakdown of piezoelectric membrane, various measures have been taken.
For example, Patent Document 1 describes that moisture intrusion into piezoelectric membrane is prevented by disposing an electrode with low water vapor permeability on the piezoelectric membrane as well as disposing protective membrane consisting of inorganic material and covering the periphery of the electrode and piezoelectric membrane.
In addition, Patent Document 2 describes that the thickness of an insulation layer made only by electrodepositing and baking (electrodeposition coating) acrylic lacquer or the like on the outer surface of a laminated piezoelectric actuator is insufficient, and therefore moisture intrusion from corner part is suppressed by performing second electrodeposition coating after electrodeposition coating of the lacquer.
Further, Patent Document 3 describes that a piezoelectric element for an inkjet head having microcracks occurred during slicing process is coated with epoxide-based adhesive to fill the microcracks and thereafter the epoxide-based adhesive is dried and hardened in order to improve its strength and make it moistureproof.
Furthermore, Patent Document 4 describes that migration of electrode material and short circuit is prevented by coating an internal electrode layer and the exposed area of an external electrode with silicone and harden the silicone to make it an exterior component.